The boom in cellular telephone usage and other forms of wireless communication has dramatically increased the number of transmission towers employed today. These towers frequently are guyed, with multiple elongated wire braces spaced about the base of a tower supporting and assisting in counteracting the effects of upper-level winds on the position and integrity of the tower. Several wire braces may terminate in a device such as an equalizer plate, to which a steel rod, typically (although not necessarily) ten to fourteen feet long, is connected at one end. In such situations the other end of the rod may be embedded in concrete and implanted in the ground, thus serving to anchor its associated wire braces and thereby moor the tower.
These anchor rods may, of course, have flaws existing as a consequence of their formation. The acts of connecting an end to an equalizer plate, embedding the opposite end in concrete, and burying a rod partially underground may also create cracks or other flaws in the rod. Because subjected to concrete, soil, and groundwater in use, the anchor rods--even if initially without flaws--further may corrode over time. Wind-related vibrations of the rods additionally cause wallows, or depressions circumscribing their circumferences, in the ground beginning at their entry points therein, so that potentially-harmful surface water may traverse the entire subterranean lengths of the rods.
As the absolute number of guyed structures increases, so too does the number of failures of rods used to anchor the guy wires. According to the December 1995 issue of Cellular Business magazine, in the preceding five years approximately nine guyed towers failed because of anchor corrosion. See K. Boney, "Getting a Grip on Towers," Cellular Business, December 1995, pp. 42, 46, 48, 52. A study commenced after an injury-causing tower collapse in 1990
found that 50% to 75% of (anchors) show some signs of corrosion . . . Of that 50% to 75%, maybe 5% to 10% have been corroded to the point that their structural integrity is in question. PA1 Because anchors are built to support specific capacity load, any corrosion also leaves the anchor overstressed. If a 1-inch round steel anchor shaft is corroded to 0.9" or 0.95" instead of its full-inch design, the structural integrity of that anchor is compromised.
Id. at p. 42.
Historically, structural integrity of buried anchor rods was not routinely assessed. As described in Cellular Business, "buried anchors used to be `out of sight, out of mind.` People didn't see them, so they didn't worry about them." Id. When assessment was necessary, the conventional technique for doing so involved excavating the soil in which a rod was set in order to examine some or all of its length visually. of course, excavating the soil about a rod decreases its load-bearing capability, destabilizing the associated tower until the soil can be replaced. Contacting a galvanized rod with metallic digging equipment, for example, might also damage the rod, and disturbing carcinogenic tars coated on rods might preclude replacement of the soil under existing environmental rules and regulations. Further, of course, mere visual examination of a rod may not result in detection of myriad types of flaws possibly present in it.